Llewellyn D Densmore

Llewellyn D Densmore
Texas Tech University | TTU · Department of Biological Sciences

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384
Publications
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Publications

Publications (384)
Article
Climate change and habitat degradation are recognized as serious threats for wildlife and an important aspects to be considered in conservation biology. However, little is known about how such environmental changes might impact crocodylians inhabiting the Neotropics and the effectiveness of Protected Areas (PAs) for long-term species conservation....
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There are few studies that have investigated the evolutionary history of large vertebrates on islands off the Caribbean coast of South America. Here we use the spectacled caiman (Caiman crocodilus) to investigate among- and within-population patterns of genetic diversity to understand connectivity between island and mainland populations. The specta...
Article
The Critically Endangered gharial (Gavialis gangeticus) residing within Bardiya National Park (BNP) in Nepal constitutes the sixth major sub-population of this unique lineage; however, this population is not well studied. A 46 km protected stretch of the Babai River and a 60 km stretch of the Karnali River in and around BNP were surveyed for gharia...
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Population ecology studies on spectacled caimans (Caiman crocodilus) in Colombia have been few and far between with many covering short periods and defining population parameters based on relative indices (i.e., individuals/km). This reflects a lack of information on the general effects that environmental variables have on annual cycles of populati...
Chapter
The order Crocodylia contains the sole reptilian survivors of the Archosauria, which also includes the dinosaurs and birds. While the living forms are not nearly as diverse as they have been in the past, they represent a lineage that first appeared in the Mesozoic Era, and that has successfully survived a number of extinction events. They also repr...
Chapter
During the late twentieth and early twenty-first centuries, there has been a revolution in evolutionary biology. Traditional methods that had been applied to understanding relationships and natural history for hundreds of years have been supplemented (and sometimes replaced) by biochemical and molecular techniques that now allow us to examine the e...
Article
Population numbers of the American crocodile in Colombia have shown an increasing trend during the last decades. However, the lack of monitoring programs has restricted our understanding about this species' ecology, limiting the ability to develop sound conservation plans. We assessed the effectiveness and robustness of the Individual Identificatio...
Article
Conservation efforts have allowed American crocodile (Crocodylus acutus) populations to recover to the point that dispersal movements are beginning to be documented. The environmental authority of San Andres Island in Colombia reported, for the first time, the arrival of two C. acutus from unknown localities in 2012 and 2018. The former was sacrifi...
Article
The Apaporis caiman (Caiman crocodilus apaporiensis) has been of particular interest due to its highly differentiated morphology. However, no molecular research has been done to clarify its taxonomy. We characterized the genetic variation within C. crocodilus by assessing the evolutionary trajectory of Apaporis caiman populations using mitochondria...
Article
Conservation efforts have allowed American crocodile (Crocodylus acutus) populations to recover to the point that dispersal movements are beginning to be documented. The environmental authority of San Andres Island in Colombia reported, for the first time, the arrival of two C. acutus from unknown localities in 2012 and 2018. The former was sacrifi...
Article
Crocodylians are large predators and ecological keystone species in wetland ecosystems. In Bolivia a total of five species occur, all of which are members of the family Alligatoridae: Caiman yacare, C. latirostris, Melanosuchus niger, Paleosuchus palpebrosus, and P. trigonatus. Beginning in the mid-1800s, wild populations were reduced and threatene...
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Reliable estimates of crocodylian population size are desirable for both understanding the ecology and natural history of species and developing sound conservation and management plans. However , choosing appropriate methods to estimate population numbers can be difficult due to the paucity of comprehensive analyses regarding their effectiveness, r...
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Studies on food habits are fundamental to understanding the ecology of a species and its interactions with the community to which it belongs. Among crocodylians, diet affects a variety of biological, physiological, and behavioral characteristics. However, despite having one of the largest distributions across the Americas, some aspects of Crocodylu...
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Identification of individuals based on morphological patterns is a strategy used primarily in human forensics that has also been applied successfully in several wildlife scenarios. To date, no study has evaluated the potential of these techniques on American Crocodiles (Crocodylus acutus). We assessed whether the dorsal scute number and pattern of...
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Conservation of large predator species has historically been a challenge because they often overlap in resource utilization with humans; furthermore, there is a general lack of in-depth knowledge of their ecology and natural history. We assessed the conservation status of the Orinoco crocodile (Crocodylus intermedius), defining regional habitat pri...
Chapter
The ethos and methods of modern science are supported by freedom and the pursuit of truth and respect for all life forms and the environment; all these are consistent with scientists’ values, and are upheld by integrity, reverence for liberty, and commitments to sustainability. Science and its ethical underpinnings are threatened by deception, delu...
Chapter
Researchers should understand the ethical principles, laws, regulations, and university policies undergirding research with human subjects, animals, biohazards, hazardous chemicals, and laboratory safety. Human subjects research requires approval of Institutional Review Boards, compliant with the Code of Federal Regulations. Animal research require...
Chapter
Steps can be taken to avoid the anxiety that may accompany thesis and dissertation preparations. The preparation approaches for dissertations include late preparation, composite, and hierarchical methods, offering varying benefits and risks. Theses and dissertations are encyclopedic in nature, including an extensive survey of the literature. The ma...
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Learning to teach well enhances communication skills. Moreover, graduate researchers with teaching skills fare better in hypothesis generation and research design. Becoming a good teacher is also essential for those researchers anticipating a career in academia, where teaching responsibilities will generally increase, going from highly research-int...
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Graduate researchers should understand the needs and methods for obtaining grant support, beginning with different vehicles for research support, from gifts to grants, to cooperative agreements, to contracts, to fellowships and scholarships. Researchers should also know about the agencies that support research, from corporations to foundations, to...
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Becoming a creative researcher involves choices, including fields and types of research, advisors, role models and support, graduate program components, a research problem, and thesis or dissertation committee members. The research choice may include personal interests, aptitudes, and career goals involving considerations of the basic or applied as...
Chapter
Scientists discover, confirm, and communicate new knowledge – all involving understanding of the requirements and skills of presenting at scientific meetings and publishing papers in the scientific literature. Presentation preparations include the development and timely submission of abstracts and conference reports, careful crafting of materials (...
Chapter
Careers are built on excellent initial positions. Landing opportunities requires planning, interview seeking, interviewing, and strategies for accepting and refusing offers. Researchers should plan early, considering sector(s) of employment, location, and professional needs, including the choice of a postdoctoral position, as assisted by publicatio...
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Productive researchers require time management, which includes planning and methods for organizing and executing plans. The plans revolve about goals: lifetime, intermediate, and short term. Goals should be written, clear, and measurable. A list of intermediate and short-term goals becomes a To Do List that is prioritized according to importance an...
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History confirms the benefits of science and scientific research. The scientific method includes observation, hypothesis development and testing, experimentation, and interpretation. Observation should include introspection that helps in defining and solving problems, and synthesizing information to differentiate the old from the new, the profound...
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Productive and rewarding research is facilitated by dedicated efforts and experience, influenced by attitudes and commitments. Of importance is the adoption of a take-charge attitude along with a commitment and desire to be creative and productive in research – all supported by priority consciousness about research, and persistence in research and...
Chapter
Career planning should begin in graduate school. Thinking 5 or 10 years ahead is helpful in attaining career goals. The planning efforts are augmented by individual development plans (IDPs). One Internet-based program, dubbed myIDP, can be used for self-assessment, judging destination options, setting goals, and designating a mentoring team. The de...
Chapter
Entering graduate school marks a turning point in many lives. Graduate education is designed for individual development and growth. With commitment, hard work, and some guidance, students become independent scholars and researchers. For many, the choice of attending graduate school begins with independent exploration as a baccalaureate student, inc...
Chapter
Expanding reading skills and abilities to use library resources are necessary for the researchers’ progress. Reading helps by stimulating ideas, improving and organizing knowledge, avoiding duplication of accomplished work, and reinforcing or refuting hypotheses. Librarians can assist the learning of library resources. Learning includes understandi...
Chapter
Graduate researchers need approaches and styles that will enhance their effectiveness in written and oral communications. Improvement requires attention to the elements of good writing, methods for improving writing skills, and tips on writing specific pieces. Writing is aided by outlines, revising and rewriting, avoiding jargon, using university w...
Article
Increasingly, endangered vertebrate species are being maintained in captive breeding programs as a method of ensuring their survival. Despite these increasing numbers of captive breeding colonies, there have been few studies designed to examine the long-term success of these programs at maintaining genetic diversity. To elucidate the effectiveness...
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Full-text available
As apex predators in their respective ecosystems, crocodylians (alligators, caimans, crocodiles, and Gharials) are facing on increased risk of extinction due to habitat encroachment by human settlements and a general lack of appreciation for their value to the ecosystem. In combination, these two major problems are reducing and shrinking crocodylia...
Article
Full-text available
Conservation of large predators has long been a challenge for biologists due to the limited information we have about their ecology, generally low numbers in the wild, large home ranges and the continuous expansion of human settlements. The American crocodile (Crocodylus acutus) is a typical apex predator, that has suffered from all of these charac...
Data
Trajectories, movement distances, and speed of the American crocodile by size class. Number of path trajectories (N), time average between locations (TAG), average movement distance (AMD), and average movement speed (AMS) followed by American crocodiles in Coiba Island per size class. (DOCX)
Data
Conspecific proximity among American crocodiles by size class. Number of observations, percent of geolocations closer than 200 m, and average conspecific proximity (ACP) within a time overlapping of 6 h estimated for 24 American crocodiles followed in Coiba Island from 2010 to 2013 divided by size class. (DOCX)
Data
Home range and utilization distribution. Utilization distribution per size classes using Kernel Density Estimation (KDE). (TIF)
Data
Home range and utilization distribution of the American crocodiles by size class. Home range and utilization distribution of the American crocodiles on Coiba Island estimated via Minimum Convex Polygon (MCP), Kernel Density Estimation (KDE), and Local Convex Hull—adaptive (aLoCoH). These values were estimated based on the average by individual + SD...
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Full-text available
We assessed the reproductive ecology of the American crocodile (Crocodylus acutus) on Coiba Island, Panama from January–December 2013. We examined nest site characteristics from January–April and hatchling survivorship from April–December. Ten nests were examined at three nesting localities where 30% of the nests were found under forest canopies an...
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We conducted nocturnal surveys in the insular and coastal areas of Coiba National Park (CNP) and its mainland buffer zone in Panama (Chiriquí conservation site) from 2009–2012 to determine the conservation status of Crocodylus acutus. In 99 nights, we surveyed 147.2 km and captured 185 animals during nocturnal transects inspection with headlamps. O...
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Along with the Orinoco and Cuban Crocodiles (Crocodylus intermedius and Crocodylus rhombifer), the American Crocodile (Crocodylus acutus) is among the most threatened crocodylian species in the Americas. Although this species is distributed widely, its IUCN “threat category” in several countries is “of concern.” We review the literature dealing wit...
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We tested microsatellites that were developed for the saltwater crocodile (Crocodylus porosus) for cross-species amplification and to provide an estimate of inter- and intraspecific variation among four species of Neotropical crocodiles (C. rhombifer, C. intermedius, C. acutus, and C. moreletii). Our results indicated that with the exception of 2 l...
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Among the loss of genetic diversity due to population declines, population fragmentation and habitat loss, hybridization also stands as a threat to Morelet’s crocodile (Crocodylus moreletii) populations. Genetic surveys in Belize and the Yucatan Peninsula have detected evidence of hybridization with the American crocodile (C. acutus). Admixture bet...
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Nerodia harteri is a threatened small-bodied water snake that occupies one of the most restricted ranges of any snake within the continental United States. It is found closely associated with rivers and tributaries in the Colorado and Brazos river basins, which flow through north-central Texas. Nerodia harteri has been at the center of debate owing...
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Two species of Ratsnake (Elaphe bairdi and Elaphe obsoleta) inhabit different environments in Texas but come into contact with one another on the southwestern edge of the Edwards Plateau. Morphological intergrades have been described by previous studies, yet no genetic evidence of hybridization has ever been reported. We tested for evidence of hybr...
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The International Crocodilian Genomes Working Group (ICGWG) will sequence and assemble the American alligator (Alligator mississippiensis), saltwater crocodile (Crocodylus porosus) and Indian gharial (Gavialis gangeticus) genomes. The status of these projects and our planned analyses are described.
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Optimal collection and preservation protocols for fecal DNA genotyping are not firmly established. We evaluated 3 factors that influence microsatellite genotyping success of fecal DNA extracted from coyote (Canis latrans) scats: 1) age of scat, 2) preservative, and 3) diet content. We quantified genotyping success by comparing rates of allelic drop...
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The American crocodile (Crocodylus acutus) is a large apex predator with an extensive but fragmented range. Crocodylus acutus suffered a population crash and was almost extirpated from Florida (USA) during the 1970s; however, in 2007 it was federally downlisted from endangered to threatened based on an increase of suitable habitat and a growing pop...
Data
List of characters and character matrix used in this analysis. (0.06 MB DOC)
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The fossil record reveals surprising crocodile diversity in the Neogene of Africa, but relationships with their living relatives and the biogeographic origins of the modern African crocodylian fauna are poorly understood. A Plio-Pleistocene crocodile from Olduvai Gorge, Tanzania, represents a new extinct species and shows that high crocodylian dive...
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Polyphenism in larval amphibians has been related to several factors, including wetland hydroperiod, food availability, competition, and predation. Spadefoot toads (genus Spea Cope, 1866) often exhibit a trophic polyphenism by developing distinct carnivore and omnivore larval morphotypes. Using a multimodel selection approach, we investigated the i...
Article
Detecting and quantifying hybridization between endangered or threatened taxa can provide valuable information with regards to conservation and management strategies. Hybridization between members of the genus Crocodylus has been known to occur in captivity and in some wild populations. We tested for hybridization among wild populations of American...
Article
Microsatellite data were generated from hatchlings collected from ten nests of Morelet's Crocodile (Crocodylus moreletii) from New River Lagoon and Gold Button Lagoon in Belize to test for evidence of multiple paternity. Nine microsatellite loci were genotyped for 188 individuals from the 10 nests, alongside 42 nonhatchlings from Gold Button Lagoon...
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The Neotropical crocodylian species, Caiman crocodilus, is widely distributed through Mesoamerica, northern South America, and the Amazon basin. Four subspecies are recognized within C. crocodilus, suggesting some geographic variation in morphology. In this study, we utilized mitochondrial DNA (mtDNA) sequence data from 45 individuals of C. crocodi...
Article
There is a surprising lack of genetic data for the Cuban crocodile (Crocodylus rhombifer), especially given its status as a critically endangered species. Samples from captive individuals were used to genetically characterize this species in comparison with other New World crocodilians. Partial mitochondrial sequence data were generated from cyt-b...
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Full-text available
The American crocodile (Crocodylus acutus) and the Morelet's crocodile (C. moreletii) are broadly sympatric in Belize and Mexico. The presence of morphologically anomalous individuals in the overlapping range area suggests possible hybridization between these species. Analysis of 477 base pairs of the mitochondrial tRNA(Pro)-tRNA(Phe)-Dloop region...
Article
Vitellogenin induction has been widely used as a biomarker of endocrine disruption in wildlife, but few studies have investigated its use in wild reptiles living in contaminated habitats. This study examined vitellogenin induction in Morelet's crocodiles (Crocodylus moreletii) from wetlands in northern Belize contaminated with organochlorine (OC) p...